1. Field of the Invention
The present invention is related to sputtering plasma reactors for plasma vapor deposition (PVD), and more particularly, to an improved interface between a PVD target, a ceramic ring and a PVD chamber wall in the plasma reactor.
2. Description of Related Art
In modern fabrication of semiconductor integrated circuits, metals are typically deposited by physical vapor deposition (PVD) utilizing a plasma reactor. This deposition process is performed in a plasma reactor 10 illustrated in the schematic cross section in FIG. 1. The reactor 10 includes a target 12, which in conjunction with a PVD chamber wall 14 and other sealing members, forms a vacuum chamber 16. The target 12 is fixed to a target backing plate 18, behind which are located unillustrated scanning magnets and the chamber cover. At least the portion of the target 12 facing the central portion of the vacuum chamber 16 is composed of the material to be sputtered, which can be, for example, aluminum. A substrate whose surface is to be sputter deposited is supported on a pedestal (not shown) positioned in opposition to the target 12.
An insulating ring 26 between the target 12 and the PVD chamber wall 14 allow their differential biasing. The insulating ring 26 is desirably made of a ceramic material. A first O-ring 28 establishes a vacuum seal between the target 12 and the insulating ring 26 while a second O-ring 30 maintains the vacuum seal between the insulating ring 26 and an adapter ring 32 of the PVD chamber wall 14.
A gas supply system (not shown) supplies a controlled flow of various gases into the vacuum chamber 16 while a vacuum pump maintains a vacuum level at a fixed gas flow. The vacuum chamber 16 is filled with argon or other non-reactive gas to a reduced pressure. Note however that in some applications a reactive gas is additionally filled into the chamber to effect reactive sputtering. The conductive chamber wall 14, usually made of aluminum or stainless steel, is generally grounded while a DC power supply 24 applies a negative voltage of about −500V to the target 12.
The electrical bias causes the argon to discharge and form a plasma of positively charged argon ions and negatively charged electrons in the space between the target 12 and the substrate. The argon ions are electrically attracted to the negatively charged target 12 and, strike it at high enough energy to sputter target particles from the target 12. To promote uniform erosion of the target 12, a magnetron may be provided above the target. However, in some applications the magnetron might be omitted by increasing the energetic electron injection ionization of the high density electron cloud 900. A DC power setting for biasing the target 12 of 3 kW is preferred but a range of 2-5 kW and a pedestal bias voltage of −30 volts DC is believed to be satisfactory for many applications. The sputtered material travels ballistically, generally omni-directionally, and some fraction hit the substrate 20 to be deposited thereon as a thin film.
Current designs typically have the target 12 making direct contact with the insulating ring 26 located between the PVD chamber wall 14 and the target. Direct contact of the target 12 with the insulating ring 26 can cause visible scratches and black marking to occur on the target during the sputtering process. As a result, the target 12 needs to be periodically reconditioned.